xhci: tracing: Use the new __vstring() helper

Instead of open coding a __dynamic_array() with a fixed length (which
defeats the purpose of the dynamic array in the first place). Use the new
__vstring() helper that will use a va_list and only write enough of the
string into the ring buffer that is needed.

Link: https://lkml.kernel.org/r/20220705224750.172301548@goodmis.org

Cc: Mathias Nyman <mathias.nyman@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

drivers/usb/host/xhci-trace.h

@@ -28,9 +28,9 @@
 DECLARE_EVENT_CLASS(xhci_log_msg,
 	TP_PROTO(struct va_format *vaf),
 	TP_ARGS(vaf),
-	TP_STRUCT__entry(__dynamic_array(char, msg, XHCI_MSG_MAX)),
+	TP_STRUCT__entry(__vstring(msg, vaf->fmt, vaf->va)),
 	TP_fast_assign(
-		vsnprintf(__get_str(msg), XHCI_MSG_MAX, vaf->fmt, *vaf->va);
+		__assign_vstr(msg, vaf->fmt, vaf->va);
 	),
 	TP_printk("%s", __get_str(msg))
 );